A new study has found that people who begin taking anti-anxiety medications such as Xanax, Ativan or Valium after the age of 65 have a 50 percent greater chance of developing dementia within 15 years than people who have never taken this class of drugs.

Xanax, Ativan and Valium fall into a class of drugs called benzodiazepines, and are some of the most frequently used drugs in psychiatry. They are primarily prescribed to treat anxiety and sleep problems.

“Considering the extent to which benzodiazepines are prescribed and the number of potential adverse effects, indiscriminate widespread use should be cautioned against,” researchers say in the study, which was published in the British Medical Journal.

Benzodiazepines are widely prescribed for insomnia, anxiety and sedation for people over 65 in many countries, including 30 percent of this age group in France, 20 percent in Canada and Spain, 15 percent in Australia, according to the researchers. Many take this type of drug for years despite guidelines suggesting it should be limited to a few weeks, the researchers note.

Researchers carried out a study on 1,063 men and women with an average age 78 in France who were all free of dementia at the start of the study in 1987, with a planned follow-up in 20 years.

The researchers used the first five years to identify the factors leading to the first prescription for a benzodiazepine medication, then evaluated the association between the new use of this drug and the development of dementia. They also assessed the association between further benzodiazepine drug use during the follow-up period and risk of subsequent dementia.

According to the researchers, 95 of the 1,063 patients started taking a benzodiazepine medication during the study. The researchers confirmed 253 cases of dementia (23.8 percent) — 30 in benzodiazepine users and 223 in non-users.

The researchers found that the chance of dementia occurring was 4.8 per 100 person years in the group taking a benzodiazepine medication compared to 3.2 per 100 person years in the group not taking any of the drugs. A “person year” is a statistical measure representing one person at risk of developing a disease during a period of one year.

The researchers note that while many of the benzodiazepine medications remain useful for treating anxiety and insomnia, there is increasing evidence that their use may induce adverse outcomes in the elderly, such as serious falls, fall-related fractures and, now, dementia.

They say that their findings add to the accumulating evidence that the use of these drugs is associated with increased risk of dementia and, if true, that this “would constitute a substantial public health concern.”

The researchers recommend that physicians should assess expected benefits of the drugs and limit prescriptions to a few weeks. They caution against “uncontrolled use.”

They conclude that further research should “explore whether use of benzodiazepine in those under 65 is also associated with increased risk of dementia and that mechanisms need to be explored explaining the association.”